GB2410282A

GB2410282A - Water management system

Info

Publication number: GB2410282A
Application number: GB0401180A
Authority: GB
Inventors: Howard Lloyd Robinson; Colin Andrew Loveday; Nicholas Paul Toy; Benjamin John Sealey
Original assignee: Tarmac Ltd
Current assignee: Tarmac Ltd
Priority date: 2004-01-20
Filing date: 2004-01-20
Publication date: 2005-07-27
Anticipated expiration: 2024-01-20
Also published as: GB0401180D0; GB2410282B

Abstract

The water management system, primarily for managing storm water over a surfaced area, includes a permeable surface course 11 comprising porous concrete including a strengthening additive capable of withstanding traffic loading in excess of 20 million standard axles and a permeable understructure 12 beneath the surface course which includes a porous foundation, there being a drainage conduit 15 from the foundation layer to beyond the boundary of the surfaced area. The strengthening additive may comprise any of a microsilica additive, an epoxy resin additive, a styrene butadiene additive, an acrylic additive or a combination of two or more of these additives. The strengthening additive is preferably a microsilica additive which comprises microsilica particles having a particle size of approximately 0.1-0.2 microns and which is added to the concrete as a microsilica slurry. The understructure preferably includes a permeable supporting structure which may have one or more layers of porous concrete and/or porous asphalt. The system also preferably includes one or more semi-permeable membranes and the foundation layer may include a filter layer of particulate material with interstitial cavities between the particles.

Description

24 1 0282 PATENTS ACT 1977 A11049GB Title: Water Management System

Description of Invention

This invention relates to a water management system for managing storm water and/or spillage on a surfaced area.

As a result of an increasing proportion of the land surface being surfaced, particularly in urban regions, an increasing proportion of storm water lO is dealt with by draining immediately directly into man- made drains and into water courses and the like, thus placing a high burden on such drainage systems. In contrast, in unsurfaced areas, the water may pass into and dwell in the ground and seep into water courses and the like over a longer period.

Moreover storm water which runs off surfaced areas is not naturally cleansed by bacteria and the like action, as is water which passes into the ground. As a result, water courses and the like can become rich with contaminants which otherwise would have been cleansed from the water.

It leas been proposed in GB patent 2294077 to provide a paved surface course through which water may pass into a substrate beneath. A water impermeable membrane is provided beneath the substrate, which membrane contains particles of the substrate in which water passing through the paved surface course may dwell. Drains from the substrate for the water are also provided. The use of an impermeable membrane restricts the capacity of the system, in that, in the event of a particularly heavy fall of water, the volume contained by the membrane may fill up, and thus water will need to be discharged via the drains. This contributes to the burden imposed on local drainage systems by run-off water from other surfaced areas.

In accordance with the present invention we provide a water management system for managing storm water over a surfaced area, the system ei. '. . : . : :e including a permeable surface course comprising porous concrete including a strengthening additive capable of withstanding traffic loading in excess of 20 million standard axles, a permeable understructure beneath the surface course, the permeable understructure including a porous foundation layer, there being a drainage conduit from the foundation layer to beyond the boundary of the surfaced area.

Such a system can be described as 'heavy duty', i.e. it can be used in applications where the traffic on the system will substantially comprise heavily laden commercial vehicles. The term 'million standard axles' is defined in the Highways Agency Design Manual, Roads and Bridges, volume 7, Pavement Design and Maintenance. The use of a strengthening additive allows the system to be used in heavy duty applications. The strengthening additive may be used to, for example, improve the strength of the porous concrete, and/or improve the wear resistance of the porous concrete, and/or improve the cohesion of the porous concrete, and/or increase the speed of cementing of the porous concrete, and/or decrease the shrinkage of the porous concrete as it dries. For example, the strengthening additive may increase the strength of the porous concrete for example by two-fold, and increase the speed of cementing of the porous concrete for example achieving the desired compressive strength within 7 days as opposed to 28 days as is the common practice.

With the system of the invention, water may exit the system into the ground beneath the system as well as through the drainage conduit, and thus the system of the invention provides the advantages of the system disclosed in GB 2294077 whilst overcoming a major problem with this system.

The strengthening additive may comprise, for example, any of: a microsilica additive, an epoxy resin additive, a styrene butadiene additive, an acrylic additive, a combination of two or more of these additives.

In a preferred embodiment, the strengthening additive comprises a microsilica additive.

: .e : . :: . : :e The microsilica additive may comprise microsilica particles having a particle size in the range of approximately O.lmicrons to approximately 0.2microns.

The microsilica additive may be added to the porous concrete as a microsilica slurry. The microsilica slurry may comprise approximately 50% microsilica powder and approximately 50% water. The microsilica slurry may comprise, for example, the Elkem Emsac 500S microsilica slurry.

The microsilica additive may comprise approximately 5% to approximately 15% by weight of cement in the porous concrete.

The porous concrete may comprise the strengthening additive and a concrete mix. The concrete mix may comprise cement, water and aggregate.

The strengthening additive is preferably, as far as possible, dispersed throughout the concrete mix of the porous concrete.

The cement may comprise Portland Cement 42.5N. The cement may comprise a mixture of Portland cement and ground granulated blastfurnace slag or pulverised fly ash. The cement may comprise approximately 15% to approximately 21% by mass of the concrete mix of the porous concrete. The water to cement ratio of the concrete mix may lie in the range approximately 0.35 to approximately 0.45.

The aggregate may comprise coarse aggregate, for example, any of: gravel, limestone, basalt, granite, slag, dolerite, a combination of two or more of these aggregates. The coarse aggregate may comprise a single size gravel, preferably comprising gravel particles having a particle size of approximately 1 Omm. The coarse aggregate may comprise approximately 65% to approximately 70% by mass of the concrete mix of the porous concrete. The use of such coarse aggregate will allow water to effectively drain through the porous concrete, but could have a tendency to decrease the strength of the porous concrete. However, in this case, this is not a problem, as any decrease in the strength is counter-balanced by the use of the strengthening additive.

: :' . ^ -:: - .: A: .. - : :e . Additionally, the aggregate may comprise fine aggregate, for example, sand, and/or crushed rock fines such as limestone. The fine aggregate may comprise approximately 5% by mass of the concrete mix of the porous concrete. The use of fine aggregate increases the compressive strength of the porous concrete.

The porous concrete may have a compressive cube strength after 3 days of approximately 23N, a compressive cube strength after 7 days of approximately 30N, and a compressive cube strength after 28 days of approximately 50N. The porous concrete may have a flexural strength after 28 days of approximately 5N. The porous concrete may have a measured plastic density of approximately 2004kgm3. The porous concrete may have a hardened density after 7 days of approximately 2145kgm3. The porous concrete may have a hydraulic conductivity in the range approximately 400 to approximately 1550Qre'. The porous concrete may have a yield of approximately 99.3%. The porous concrete preferably has a minimum air void content of approximately 15%. This percentage allows adequate water flow through the concrete. The porous concrete preferably has good resistance to scuffing, for example no wear after a 2 hour vehicle tyre scuffing test at 45 C (as devised by the Transport Research Laboratory).

The surface course may have a thickness in the range approximately 100mm to approximately 300mm, preferably approximately 150mm. The thickness used for the surface course may be chosen depending upon the traffic loading for which the system is intended.

A top surface of the surface course may be textured and/or coloured, suitable for its particular use, for example to provide for increased skid resistance. The surface course may include an overlay of porous asphalt. The overlay of porous asphalt may have a thickness of approximately 30mm. This may be used to improve the ride quality and skid resistance and decrease the traffic noise of the water management system.

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The understructure may include a permeable supporting substrate. The supporting structure may be provided between the surface course and the foundation layer. The supporting substrate may include one or more layers.

The supporting structure may include one or more layers of porous concrete. The or each or some of the layers of porous concrete may include a strengthening additive.

The supporting substrate may include one or more layers of porous asphalt. When the supporting substrate includes one layer of porous asphalt, the layer of porous asphalt may include an aggregate of asphalt, in which all the particles are able to pass through any one of a 40mm sieve or a 28mm sieve or a 20mrn sieve. When the supporting structure includes more than one layer of porous asphalt, the layers may include aggregates of asphalt which have the same particle size, for example particles which are able to pass through any one of a 40mm sieve or a 28mm sieve or a 20mm sieve. When the supporting structure includes more than one layer of porous asphalt, the layers may include aggregates of asphalt which have different particle sizes, for example particles which are able to pass through a 40mm sieve or a 28mm sieve or a 20mm sieve.

The particle size of the aggregate of asphalt of a topmost layer may be less than the particle size of the aggregate of asphalt of the or each layer beneath the topmost layer. For example, the supporting substrate may include an upper layer of porous asphalt which includes an aggregate of asphalt in which all the particles are able to pass through a 28mm sieve and preferably a 20mm sieve, and a lower layer of porous asphalt which includes an aggregate of asphalt in which all the particles are able to pass through a 40mm sieve. The or each or some of the layers of porous asphalt may include a penetration grade bitumen, such as 160/220 grade bitumen or 100/150 grade bitumen. The or each or some of the layers of porous asphalt may have a thickness of between 30mm and 80mm.

;. :.e . hi: The water management system may comprise one or more semi- permeable membranes. For example, a semi-permeable membrane may be provided between the surface course and the foundation layer, and/or beneath the foundation layer. The or each semi-permeable membrane may be of a kind of membrane which permits the passage of water therethrough and which substantially prevents the passage of contaminant particles into the foundation layer and ground beneath. For example, the or each semipermeable membrane may be a synthetic geo-textile membrane. Thus contaminants will dwell in the permeable supporting substrate and this will give time for bacteria and the like to cleanse the contaminants.

The foundation layer may include a filter layer of particulate material with interstitial cavities between the particles. The particle sizes may vary such that all of the particles are able to pass through a 300mm sieve but none of the particles are able to pass through a 6mm sieve. The foundation layer may have a thickness of at least 200mm, and preferably of approximately 300mm, but may have a greater thickness as required. The foundation layer may be laid on a natural or laid sub-grade.

The drainage conduit may extend to a man-made or natural drain. or may be a simple soak away, but in each case, preferably the drainage conduit extends into the foundation layer and has passages for water from the foundation layer through walls of the conduit.

An embodiment of the invention will now be described with reference to the accompanying drawing, which is a schematic section through a water management system in accordance with the present invention.

Referring to the drawing a water management system 10 for a surfaced area includes a permeable surface course 11, and an understructure including a porous foundation layer 12, which is laid on a natural or man-made subgrade 13. A semi-permeable membrane 14 is provided beneath the foundation layer 12. One or more drainage conduits 15 extend from the foundation layer 12 : .. : . :. :.e.. :e:e. -

beyond a boundary of the surfaced area over which water is managed by the system 10 of the present invention.

The design and construction of each of the layers is critical to proper performance of water management for the surfaced area and thus the makeup S of each of the layers will now be described.

The permeable surface course 11, comprises porous concrete including a microsilica additive and a concrete mix. The concrete mix comprises cement, water and aggregate. The microsilica additive comprises microsilica particles having a particle size in the range of approximately 0. [microns to approximately 0.2microns. The microsilica additive is added to the porous concrete as a microsilica slurry, for example the Elkem Emsac SODS microsilica slurry, and, as far as possible, is dispersed throughout the concrete mix. The microsilica additive comprises approximately 5% to approximately 15% by weight of the cement in the concrete mix. The cement is Portland Cement 42.5N, and makes up approximately 15% to approximately 21% by mass of the concrete mix. The water to cement ratio of the concrete mix is in the range 0.35 to 0.45. The aggregate comprises a coarse aggregate of single size gravel, comprising gravel par icles having a particle size of approximately 1 Omm. The gravel makes up approximately 65% to approximately 70% by mass of the concrete mix. The aggregate further comprises a fine aggregate of sand, which makes up approximately 5% by mass of the concrete mix.

This results in a porous concrete having the following physical properties, a compressive cube strength after 3 days of approximately 23N, a compressive cube strength after 7 days of approximately 30N, and a compressive cube strength after 28 days of approximately SON, a flexural strength after 28 days of approximately SN, a measured plastic density of approximately 2004kgm3, a hardened density after 7 days of approximately 2145kgm3, a hydraulic conductivity in the range of approximately 400 to approximately 1550Qre, a yield of approximately 99.3%, a minimum air void e e e e. e e e e e e content of approximately 15%, and good resistance to scuffing, for example no wear after a 2 hour vehicle tyre scuffing test at 45 C.

The permeable surface course 11 of porous concrete may have a slab thickness of between lOOmm and 300mm, preferably 150mm. If desired, the S permeable surface course of porous concrete may include an overlay of porous asphalt. Furthermore, the top surface of the surface course 11 may be textured as desired, for example to provide improved skid resistance/grip for pedestrian and/or vehicular traffic on the surfaced area.

The porous concrete may be laid in a Plowable state, and preferably is allowed to set without compaction, or at least without the degree of compaction typically employed when laying non-porous concrete, to provide the surface course 1 1.

The porous concrete of the surface course 11 permits storm or spillage water on the surfaced area to pass through the surface course 11 to the porous IS foundation layer 12 beneath. The microsilica additive strengthens and increases the speed of cementing of the porous concrete.

If desired, the permeable surface course 11 may include a plurality of permeable layers, rather than the single layer construction described with reference to the drawing. If desired, the understructure may comprise a permeable supporting substrate, which may comprise one or more layers of, for example, porous concrete with or without a strengthening additive, and/or porous asphalt.

The foundation layer 12 beneath the surface course 11, is provided by particulate material which may be natural rock, such as limestone, and/or a recycled material such as crushed concrete/brick or an industrial coproduct such as slag, for examples only. The particle sizes of the foundation layer 12 may vary such that all of the particles are able to pass through a 300mm sieve but none of the particles are able to pass through a 6mm sieve. The foundation : .e :. . ...

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layer 12 may have a thickness of at least 200mm and preferably of approximately 300mm, but may have a greater thickness as required.

The particles of the foundation layer 12 provide a filter for water passing through the foundation layer 12, the particles providing between them, interstitial cavities in which water may dwell, whilst bacteria for example, may naturally cleanse the water. Slowly the water may drain through the filter foundation layer 12 to the sub-grade 13. However, to provide for the escape of water from the system 10, within the foundation layer 12 there are provided drainage conduits 15 (only one is shown in the drawings), which in this example are of the kind having through walls thereof, passages (smaller than the minimum particle size of 6mm of the material of the foundation layer 12) or being porous to permit water to drain through the walls and into the interiors of the conduits 15. The conduits 15 extend downwardly to and outwardly beyond a boundary of the surfaced area over which water is to be managed by the system 10 of the invention, and in one embodiment, the conduits 15 connect with man-made drains or a natural water course, or the drainage conduits 15 may simply permit the drained water to soak away into the ground, beyond the surfaced area. Howeverif desired, the conduits 15 may include a drainage control valve to enable the rate of water drainage from the foundation layer 12 to be controlled, or the rate of drainage may be restricted by reducing the cross sectional dimension of the interior flow passages of the conduits 15. In each case preferably the rate of drainage is controlled so that water tends to dwell sufficiently long in the filtering foundation layer 12 for the water naturally to be cleansed, before the water is released to the sub-grade 13 beneath or passes from the system 10 via the drainage conduits 15.

The semi-permeable membrane 14 may be made of any suitable material with passages for water, but the passages are of a sufficiently small size that the semi-permeable membrane 14 retains particulate contaminants which may pass from the surface course 11, and through the foundation layer 12. One suitable : : . . ...

e,: .. :. :. . material for the semi-permeable membrane 14 is a woven geotextile material, made of a synthetic material with passages for water which are not readily perceivable to the naked eye.

In another example, the semi-permeable membrane 14 need not be provided. By careful design and construction of the various layers, water may be retained in the system and released in a controlled manner into the sub grade 13 and into the drainage conduits 15.

When used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

: : - . . . . :. :.: .. :. :. .

Claims

1. A water management system for managing storm water over a surfaced area, the system including a permeable surface course comprising porous concrete including a strengthening additive capable of withstanding traffic loading in excess of 20 million standard axles, a permeable understructure beneath the surface course, the permeable understructure including a porous foundation layer, there being a drainage conduit from the foundation layer to beyond the boundary of the surfaced area.

2. A system according to claim 1 in which the strengthening additive comprises any of: a microsilica additive, an epoxy resin additive, a styrene butadiene additive, an acrylic additive, a combination of two or more of these additives.

3. A system according to claim 2 in which the strengthening additive comprises a microsilica additive, which comprises microsilica particles having a particle size of approximately 0. [microns to approximately 0. 2microns.

4. A system according to claim 2 or claim 3 in which the strengthening additive comprises a microsilica additive, which is added to the porous concrete as a microsilica slurry, such as the Elkem Emsac 500S microsilica slurry.

5. A system according to any of claims 2 to 4 in which the strengthening additive comprises a microsilica additive, which comprises approximately 5% to approximately 15% by weight of cement in the porous concrete.

6. A system according to any preceding claim in which the porous concrete comprises the strengthening additive and a concrete mix.

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7. A system according to claim 6 in which the concrete mix comprises cement, water and aggregate.

8. A system according to claim 7 in which the cement comprises approximately 15% to approximately 21% by mass of the concrete mix.

9. A system according to claim 7 or claim 8 in which the water to cement ratio of the concrete mix lies in the range approximately 0.35 to approximately 0.45.

10. A system according to any of claims 7 to 9 in which the aggregate comprises a coarse aggregate of any of: gravel, limestone, basalt, granite, slag, dolerite, a combination of two or more of these aggregates.

11. A system according to claim 10 in which the coarse aggregate comprises a single size gravel, comprising gravel particles having a particle size of approximately lOmm.

12. A system according to claim 10 or claim 11 in which the coarse aggregate comprises approximately 65% to approximately 70% by mass of the concrete mix.

13. A system according to any of claims 10 to 12 in which the aggregate comprises a fine aggregate of sand.

14. A system according to claim 13 in which the sand comprises approximately 5% by mass ofthe concrete mix.

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15. A system according to any preceding claim in which the porous concrete has a compressive cube strength after 3 days of approximately 23N, a compressive cube strength after 7 days of approximately 30N, and a compressive cube strength after 28 days of approximately 50N.

16. A system according to any preceding claim in which the porous concrete has a flexural strength after 28 days of approximately 5N.

17. A system according to any preceding claim in which the porous concrete has a measured plastic density of approximately 2004kgm3.

18. A system according to any preceding claim in which the porous concrete has a hardened density after 7 days of approximately 2145kgm3.

19. A system according to any preceding claim in which the porous concrete has a hydraulic conductivity in the range approximately 400 to approximately 1550Qrel.

20. A system according to any preceding claim in which the porous concrete has a yield of approximately 99.3%.

21. A system according to any preceding claim in which the porous concrete has a minimum air void content of approximately 15%.

22. A system according to any preceding claim in which the porous concrete has good resistance to scuffing, for example no wear after a 2 hour vehicle tyre scuffing test at 45 C.

: :- . . . . :e:.: .. .:e:. .

23 A system according to any preceding claim in which the surface course has a thickness of between l OOmm and 300mm, preferably 150mm.

24. A system according to any preceding claim in which the understructure includes a permeable supporting substrate, provided between the surface course and the foundation layer.

25. A system according to claim 24 in which the supporting substrate includes one or more layers.

26. A system according to claim 25 in which the supporting substrate includes one or more layers of porous concrete.

27. A system according to claim 26 in which the or each or some of the porous concrete layers include a strengthening additive.

28. A system according to any of claims 25 to 27 in which the supporting substrate includes one or more layers of porous asphalt.

29. A system according to any preceding claim which further comprises one or more semi-permeable membranes.

30. A system according to any preceding claim in which the foundation layer includes a filter layer of particulate material with interstitial cavities between the particles.

31. A system according to claim 31 in which the particle sizes vary such that all of the particles are able to pass through a 300mm sieve but none of the particles are able to pass through a 6mm sieve.

. . . . .: :. : .: a. ..

32. A system according to any preceding claim in which the foundation layer has a thickness of approximately 300mm.

33. A water management system for a surfaced area substantially as hereinbefore described with reference to and/or as shown in the accompanying drawings.

34. Any novel feature or novel combination of features shown described herein and/or as shown in the accompanying drawings.

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